1. Field of the Invention
The present invention relates to hybrid transmissive focalizing optical systems, more particularly for utilization in collecting solar energy.
2. Description of the Prior Art
It has been recently proposed to realize lenses or lens members, more particularly of the Fresnel type, out of plastic material so as to avoid problems, particularly of weight, inherent to the glass lenses of medium or great dimensions.
Lenses out of methyl-polymethacrylate have shown excellent properties, despite transmission losses due to remaining geometrical defects resulting from the shrinking of the utilized material, but the price thereof remains excessively high. Hybrid optical systems have also been proposed which utilize a layer of glass forming a support and a layer of plastic material out of silicone resin forming the optically active focalizing part or lens. Said hybrid systems are also very expensive and exhibit problems of mechanical aspects over a long period of utilization at the level of the interface between the two adjoined parts.